TURTL3
Well-Known Member
The SCT tuner (I have one) gives you the option to change the gear ratio - but it doesn't actually do anything, since the '15 and up Mustangs hold this info in the BCM (Body Control Module) and the SCT modified the ECU (Engine Control).
If you have an automatic transmission - the change in gear ratio will need the tune adjusted for shift points. If you already have an aftermarket tune, simply email / call them and request a change. Most of them should be well versed in making the needed changes.
If you want to more about the BCM and the changes you CAN make in there (including gear ratio) with a computer, FORSCan (Free software) and an adapter that lets you access it ($30-50 depending) check out this thread:
https://www.mustang6g.com/forums/showthread.php?t=61773
Tire / wheel size doesn't really matter unless you make drastic changes. It's all about tire diameter.
Also if you make a more drastic gear ration change - from 3.15 to say 3.73 for example - you MIGHT need to make the change in the BCM for gear ratio, as I personally don't know the limitation of the automatic compensation the ABS / Wheel sensors / system is capable of.
Clear as mud?
Keep in mind - there are 15-17 owners out there who THINK the SCT can change gear ratios - like I said it HAS the option (it just doesn't do anything, it's applicable to the older cars) but it does NOT write to the BCM where this info is stored.
Ahh ok I got it now. Having a manual makes all of this just a little easier lol
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